Red, Cream and Tortoiseshell-The O -Gene
- miriamm00
- 15 minutes ago
- 2 min read
Red, cream and tortoiseshell coat colours are coded by the “O gene” which is carried on the X chromosome. The O gene causes the normal black colour to be produced as a red pigment. O or Red is dominant. “oo” is black. A male cat who has the O gene will be red. If the O is diluted with dd then he will be cream. A female cat who is OO or has two copies of the O gene (because she has TWO X chromosomes) will be Red, and diluted will be cream. A female cat who is Oo will be tortoiseshell (that is, black patches in her coat from the “o”). She will have patches across her coat from “X-inactivation” -this is because as she develops from an embryo one of the X chromosomes is inactivated in each cell so that only one X chromosome is coding for all the proteins – this inactivation is not consistent across every cell, in some cells one X chromosome is inactivated, in other cells the other one is inactivated.
In some tortoiseshell cats you can get patches of white (a tricolour or calico cat), this comes from the “spotting gene” which produces white, unpigmented patches by delaying the migration of the melanocytes to the skin surface during embryonic development. There are a number of alleles of this gene that produce greater or lesser delays. The amount of white is divided arbitrarily into “mitted”, “bicolour”, “harlequin” and “van” going from almost no white to almost completely white. I won’t go into the differences between these 4 types of white spotting as the Burmese breed doesn’t (as yet) allow these coat patterns. Also, without going into huge detail here, the spotting gene also affects the size of the patches of white and other colours due to the effect on embryonic cell migration and X-inactivation. Essentially each patch of colour represents a clone of cells derived from one original cell in the early embryo.
The ”rufous polygenes” affect the richness of the orange or red gene expression. These are multiple genes that influence the amount and quality of eumelanin and/or phaeomelanin pigment expression.
It's commonly believed in the cat breeding community that tortoiseshell cats are more aggressive, naughty and lively and are often described as “naughty torties” – however there is very little existing scientific evidence and one study found no relationship between coat colour and tameness.
The reason that red and cream cats have barring is because of the agouti protein antagonising MC1R. If you can breed out the agouti protein gene from the cat you should be able to achieve a solid red or cream cat.
Millrock Harvest Gold (Silver Double Grand Champion) -Cream Burmese, often wins BAMs for the lack of barring and his smooth dense coat although his type is a little old fashioned with a longer wedge and flat occiput.
Comments